OBJECTIVE To evaluate the influence of prenatal conditions on the development of immune responses during infancy. RESULTS We continue to assess the way different pregnancy conditions affect the development of the nervous and immune systems of the infant monkey at birth and across the first year of life. We have shown that prenatal experiences can have long-lasting effects on many behavioral and lymphocyte responses during development, including the cellular ability to recognize and respond to nonself antigens. FUTURE DIRECTIONS To consider the relevance of these findings for understanding individual differences in postnatal immunity and response to infection. KEY WORDS infant development, prenatal, lymphocyte proliferation, natural killer cell activity FUNDING NIMH MH41659